Houang Elizabeth T S, Chu Yiu-Wai, Lo Wai-Sing, Chu Ka-Yi, Cheng Augustine F B
Department of Microbiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, China.
Antimicrob Agents Chemother. 2003 Apr;47(4):1382-90. doi: 10.1128/AAC.47.4.1382-1390.2003.
We characterized two new gene cassettes in an Acinetobacter isolate: one harbored the metallo-beta-lactamase (IMP-4) gene bla(IMP-4), the other harbored the rifampin ADP-ribosyltransferase (ARR-2) gene arr-2, and both arrayed with the aminoglycoside acetyltransferase [AAC(6')-Ib(7)] gene cassette aacA4 in two separate class 1 integrons. The epidemiology of these gene cassettes in isolates from blood cultures obtained from 1997 to 2000 was studied. Isolates bearing either the bla(IMP-4) or the arr-2 gene cassette or both represented 17.5% (10 of 57) of isolates in 1997, 16.1% (10 of 62) in 1998, 2.5% (1 of 40) in 1999, and 0% (0 of 58) in 2000. These two gene cassettes, probably borne on two separate integrons, were found in at least three genomic DNA groups, with evidence of clonal dissemination in the intensive care unit during 1997 to 1998. Seventeen of the 52 Acinetobacter baumannii (genomic DNA group 2) isolates from 1997 to 2000 harbored intI1, but only one was positive for these gene cassettes, whereas 20 of the 21 intI1-positive isolates of all other genomic DNA groups were positive for either or both of them. Reduced susceptibility to imipenem and rifampin was seen only in isolates harboring the bla(IMP-4) and arr-2 cassettes, respectively. The aminoglycoside phosphotransferase [APH(3')-VIa] gene aph(3')-VIa was detected in all 21 isolates for which the MIC of amikacin was >/=8 micro g/ml, with or without aacA4, whereas aacA4 alone was found in isolates for which the MIC of amikacin was 0.5 to 2 micro g/ml. Significant differences between the 17 intI1-positive and 47 intI1-negative isolates belonging to genomic DNA group 3 from 1997 to 1998 in the MICs of amikacin, gentamicin, imipenem, sulfamethoxazole, and ceftazidime were observed (Mann-Whitney test, P < 0.001 to 0.01).
一个含有金属β-内酰胺酶（IMP-4）基因bla(IMP-4)，另一个含有利福平ADP-核糖基转移酶（ARR-2）基因arr-2，且二者都与氨基糖苷乙酰转移酶[AAC(6')-Ib(7)]基因盒aacA4排列在两个独立的1类整合子中。我们研究了这些基因盒在1997年至2000年血培养分离株中的流行病学情况。携带bla(IMP-4)或arr-2基因盒或二者皆有的分离株在1997年占分离株的17.5%（57株中的10株），1998年为16.1%（62株中的10株），1999年为2.5%（40株中的1株），2000年为0%（58株中的0株）。这两个基因盒可能位于两个独立的整合子上，在至少三个基因组DNA组中被发现，有证据表明在1997年至1998年期间在重症监护病房有克隆传播。1997年至2000年的52株鲍曼不动杆菌（基因组DNA组2）分离株中有17株携带intI1，但只有1株这些基因盒呈阳性，而所有其他基因组DNA组的21株intI1阳性分离株中有20株其中一个或两个基因盒呈阳性。仅在分别携带bla(IMP-4)和arr-2基因盒的分离株中观察到对亚胺培南和利福平的敏感性降低。在所有21株阿米卡星MIC≥8μg/ml的分离株中均检测到氨基糖苷磷酸转移酶[APH(3')-VIa]基因aph(3')-VIa，无论有无aacA4，而在阿米卡星MIC为0.5至2μg/ml的分离株中仅发现aacA4。观察到1997年至1998年属于基因组DNA组3的17株intI1阳性和47株intI1阴性分离株在阿米卡星、庆大霉素、亚胺培南、磺胺甲恶唑和头孢他啶的MIC方面存在显著差异（曼-惠特尼检验，P<0.001至0.01）。
